No, you didn't miss it.  It's a bit less explicit than it could be, but the `>=` `&&` `<=` conditions below will never be met (hence `intersects` will never be `true`) in these cases.  The only way to intersect if the points are equal is to have `startRel` (and `endRel`) be `ol.extent.Relationship.INTERSECTING` (handled above).

I agree the check could be more explicit (we could bail out earlier).  Note that the [tests cover](https://github.com/openlayers/ol3/pull/1754/files#diff-0c5ae6d3103df4bd73579a01f2093aedR416) the two zero length segment cases.